1. DESCRIPTION (provided by applicant): Anticipated Impact on Veteran Care: This project aims to provide formerly homeless veterans with co- occurring substance abuse and mental illness an effective psycho-education peer intervention that will improve their substance use, housing retention, and community participation. If successful, the intervention will be readily transferrable and so can be used to improve Veteran housing outcomes across the nation. Background: An announced goal of the Veterans Administration (VA) is to end veteran homelessness within five years as nationally 107,000 veterans are estimated to live on streets or in shelters each night. The Housing and Urban Development - Veterans Affairs Supportive Housing (HUD-VASH) program is one of the largest of the VA housing initiatives, combining housing vouchers with case management wrap-around services for up to 20,000 individuals. Despite these efforts according to a recent national study, up to 20% of HUD-VASH residents will become homeless again over time and the majority of those will have co-occurring issues of mental illness and substance abuse. We will address this problem by implementing and testing the peer support component of The Maintaining Independence and Sobriety through Systems Integration, Outreach, and Networking (MISSION) Consumer Workbook, which is an integrated mental health and substance abuse treatment tested on homeless veterans with these co-occurring conditions (Smelson, Kline, Hills, Mizzeli & Trip, 2007). Objectives: We aim to test the impact of the peer intervention of the MISSION Consumer Workbook to improve treatment engagement, housing retention, and community functioning. Peer support technicians will augment the HUD-VASH case management services as usual in two sites: Bedford MA and Pittsburgh PA. The Consumer Workbook of the MISSION manual provides over 20 didactic and structured exercises that will be used during weekly home visits over a year. We have four objectives; 1) to examine whether MISSION derived peer support delivered in HUD-VASH programs will result in improved overall mental health status, reduction in days of substance use and greater treatment engagement; 2) to test the effect of MISSION derived peer support services on housing retention among HUD-VASH housed veterans with co-occurring conditions; 3) to examine whether the MISSION derived peer support services result in higher levels of community participation and social functioning; and 4) to conduct a formative evaluation, observing and gathering information on implementation of the peers using a mixed methods approach (including qualitative interviews and a cost tally) that will inform future trials. Methods: This project will randomly assign 200 Veterans using HUD-VASH vouchers and services who are determined to be at-risk for housing loss into two groups on a rolling admission basis. The control group that will receive HUD-VASH case management services as usual, and the intervention group will receive MISSION derived peer support services. Data will be collected for subjects on: substance use, overall mental health functioning, engagement in substance abuse treatment services, the length of time housed, and community participation. We will collect data from individuals at baseline and three time points for up to one year. We will also conduct semi-structured interviews with Veterans, peer providers and case managers, along with a cost tally for the program for a formative evaluation. Our data analysis strategy will be to use a repeated-measures model to test for the significance of the treatment-by-time interaction while accounting for the clustered design of case manager within site.